When a cathode including aluminum is used in a battery with an aqueous electrolyte, hydroxide and oxide anions generated at the anode can react with the aluminum to form a passivating aluminum oxide layer. In some cases, an electric field can draw anions through an aluminum oxide layer on the cathode, growing the oxide layer into as well as away from the surface of an electrode. Thus, the use of aluminum in cathodes can be hindered by the inability of cathodes to provide reversible insertion of aluminum ions.